1. Field of the Invention
The present invention relates to an autotensioner, and, in particular, to an autotensioner for applying proper tension to a timing belt for use in an automobile engine or to a belt for driving auxiliary equipment such as an alternator or a compressor or the like (hereinafter referred to simply as a "belt"), while controlling vibration in the belt.
2. Description of the Prior Art
A drive device using a belt 1 as illustrated in FIG. 1 is widely used to rotatably drive a cam shaft for an OHC type or a DOHC type engine in synchronism with a crank shaft. The drive device of FIG. 1 comprises a drive pulley 2 rotatably driven by an engine crank shaft, a driven pully 3 secured on the end of the cam shaft, guide pulleys or driven pulleys 4 for guiding the belt 1 or driving a piece of auxiliary equipment such as a water pump, and a pulley 5 for applying proper tension to the belt 1.
The pulley 5 is pivotably supported on a rocker member 7 which swings around a pivot shaft 6. Secured to the rocker member 7 is a bracket 8, and a spring 9 is provided on the end of the bracket 8. Specifically, in order that uniform tension is normally maintained in the belt 1 regardless of changes in the dimensions of the belt 1 as a result of temperature changes and the like, or regardless of vibrations from the operation of the engine, an elastic pressure is applied by the pulley 5 against the belt 1 by the spring 9.
This type of autotensioner must not only provide the function of providing tension on the belt 1, but also the function of controlling the belt 1. Specifically, in the drive device of the cam shaft shown in FIG. 1, the part of the belt 1 positioned between the pulleys 2 to 5 has a tendency to vibrate in the direction at right angles to the running direction during the rotation of the drive pulley 2. In the case where this vibration is allowed to continue unchecked, the amplitude of vibration becomes large (the vibration is propagated), so that there is the problem that an extremely large vibration is developed in the drive section by the belt 1, which in the case of a toothed belt, may result in disengagement of the teeth results.